[Exim] relaying...

Hey all!

I´ve been playing around with this now for a couple of hours and cannot
come to a solution...

I want exim to be setup to:
- allow incoming mail to local domains (ok, thats fine (local_domains))
- allow incoming mail to any address coming from a sender that is
mentioned in a list of senders
- reject everything else

can anyone please give me a hint on how to do this? I`ve been trying to
set this up - as I already mentioned - for the last several hours...

thanks a lot in advance,

-philipp
...desperately seeking for help ;)